The use of oximes for extracting copper from aqueous solutions is known. DE-OS 15 33 079 teaches a process fro selective extraction of copper from solutions with a low pH value. The extracting agent used is a mixture of a 2-hydroxybenzophenone oxime and an aliphatic alpha-hydroxyoxime, which is dissolved in a hydrophobic organic solvent. Adding the aliphatic oxime increases the rate of copper extraction.
DE-OS 21 25 095 relates to the selective extraction of copper, nickel, iron, and/or cobalt salts from aqueous solutions with a ketoxime which is dissolved in kerosene, toluene, or xylene. The ketoxime corresponds to the general formula R--C(.dbd.NOH)--R.sup.1, R being a straight or branched chain alkyl radical with 7 to 11 carbon atoms and R.sup.1 denoting a phenyl group carrying an OH group, in the position ortho to the radical R--C(.dbd.NOH.sub.2)--, and another R.sup.2 group. Good results are achieved with solutions containing the copper salt in concentrations of 0.05 to 0.5 moles/liter. A low pH value increases the yield of copper extracted.
According to DE-OS 23 34 901, compounds of the general formula ##STR1## dissolved in organic solvents which are immiscible in water are used for extracting copper and optionally iron, cobalt, and zinc from their aqueous solutions. The process is particularly suitable for separating copper from iron-containing solutions.
DE-OS 26 12 505 describes the separation of copper from acidic solutions by means of liquid-liquid extraction with a mixture of a hydroxyoxime of the general formula A--C(.dbd.NOH)--R (where A denotes an aromatic radical substituted in the ortho position by an OH group and R stands for a hydrogen atom or an aliphatic radical) and/or a 2-hydroxybenzophenone oxime as well as another oxime, which are dissolved in an organic solvent.
The known processes for separating copper from aqueous solutions by extraction with oximes do not fulfill all practical requirements. In particular, the completeness of the separation and/or the cost-effectiveness of the extracting agent are not always solved satisfactorily.
Therefore, the problem was to develop a process for extracting copper from aqueous solutions with avoids the above shortcomings and permits near-complete and economic separation of copper.